Towards Energy-Efficient Drinking Water Production using Biomimicry

Licentiate thesis, 2017

Water is a prerequisite for life and we therefore need pure drinking water to survive. Yet there are more than half a billion people that do not have access to pure drinking water. Water treatment can be performed in many different ways, one of the most commonly used being filtration. As the climate is getting warmer and sources of fresh water are being increasingly contaminated, attention is shifted to the sea in the search for drinking water. Sea water does, however, need to be desalinated before it is usable as drinking water. Desalination is commonly conducted using the process of reverse osmosis (RO), where water is forced to penetrate water-selective barriers in filters. The main issues with reverse osmosis are that the pressure needed to drive the process against the osmotic pressure build-up is significant and that the diffusivity of water through the selectively permeable layer is relatively slow. The energy input needed to run a reverse osmosis process using saline sea water is therefore substantial and the process is mainly performed in large-scale desalination plants. A more energy-efficient solution is needed in order to produce drinking water in a more sustainable manner as well as on a smaller scale. Nature purifies water in a variety of ways such as large-scale water passage through sand and small-scale purification conducted by mussels. The aim of this thesis was to design a water filter using inspiration from nature. The model system of choice was the water transport across the cell membrane, which is present in both animals and plants. This water transport is conducted by transmembrane proteins called aquaporins, and the aim of this thesis was to incorporate aquaporins in a design that could potentially be used for water filtration purposes. This thesis proposes a design where aquaporins are supported by mesoporous silica in order to improve robustness. A straightforward assembly process was developed and the resulting design was evaluated using a range of characterization techniques. The results showed that the mesoporous substrate greatly facilitated the spontaneous rupture and bilayer formation from proteoliposomes. Furthermore, neutron reflectivity data provided evidence of protein–silica intercalation where aquaporins made use of the aqueous pore environment to host their extracellular domains. This behavior is thought to improve the robustness of the system. The proposed water filter design put forward in this thesis will hopefully prove useful in the production of drinking water in the future.